Anatomic factors affecting microkeratome placement in laser in situ keratomileusis

Purpose: To identify the significant anatomic factors that affect placement of 2 microkeratomes and compare the ease of their placement. Setting: The Laser Center, Houston, Texas, USA. Methods: Anatomic factors affecting microkeratome placement were evaluated in 250 eyes of 137 myopic patients in a prospective consecutive-enrollment study. Anatomic factors measured included vertical orbital width, horizontal interpalpebral fissure (HPF), corneal diameter, and position of the corneal apex relative to the lateral orbital rim (PCL). Vertical orbital width and HPF were measured with a micrometer caliper (Mitutoyo); corneal diameter, with Orbscan topography (Bausch & Lomb Surgical); and PCL, with a Hertel exophthalmometer. Patients were randomly divided into 2 groups (125 eyes/group) to have surgery with the Automated Corneal Shaper(R) (ACS) (Bausch & Lomb Surgical) or Hansatome (Bausch & Lomb Surgical) microkeratome. Microkeratome placement was graded by 1 surgeon as "easy" (grades 1, 2, and 3) or "difficult" (grades 4 and 5). Results were correlated with anatomic factors to evaluate possible anatomic influences on the difficulty of microkeratome placement. Results: The PCL and vertical orbital width were statistically significant factors in predicting the difficulty of ACS microkeratome placement (P < .05). For the Hansatome microkeratome, since only 1 eye was graded as a difficult placement, the anatomic parameters affecting placement could not be evaluated. There were no statistically significant between-group differences in mean age and means of all anatomic factors measured (independent t test, P > .05). Difficult applanations were encountered in the ACS group (8/125 eyes, 6.4%) more than in the Hansatome group (1/125 eyes, 0.8%), which was a statistically significant difference by the Pearson chi-square test (P < .05). Conclusions: The PCL and vertical orbital width were significant anatomic factors affecting placement of the ACS microkeratome. The anatomic factors affecting Hansatome microkeratome placement could not be determined. The percentage of difficult placements was significantly lower with the Hansatome than with the ACS. (C) 2000 ASCRS and ESCRS.